This invention relates to a polymeric resin laminate possessing a rigid thermoplastic resin layer bonded to a thermoset resin layer and to a process and apparatus for the manufacture of the laminate.
The goal of bonding the same, similar or totally dissimilar layers of polymeric resin materials to provide a laminate product of reliable and durable performance poses a problem of materials engineering for which a practical and effective solution is often elusive. This is particularly true where a rigid thermoplastic resin layer is to be bonded to a thermoset resin layer. Even after relatively brief periods of service, contact adhesives frequently fail with consequent delamination of the component layers of the laminate article.
Frequent cycles of dynamic stress and/or thermal cycling applied to a polymeric resin laminate tend to accelerate adhesive failure. In the case of sanitary ware products such as bathtubs, sinks, etc., of laminate construction in which a rigid thermoplastic resin cosmetic layer is bonded to an underlying thermoset reinforcing layer, the problem of achieving permanent, or at least long-term, adhesion of the two layers to each other is a particularly difficult and challenging one. Similarly, in the case of laminated automotive body panels, particularly those associated with the engine compartment, wide temperature variations coupled with internal mechanical and road-induced stresses tend to accelerate the delamination process.
The chemical bonding of dissimilar organic polymer layers is known. The bonding principle involves the chemical reaction of reactive functional groups in one layer with reactive functional groups in an adjacent layer to form covalent bonds between the two layers. This approach has been used to achieve chemical bonding between a rigid thermoplastic resin layer and a thermoset resin layer. Up until now, the rigid thermoplastic resin layer has either possessed chemically reactive functional groups as part of its bulk molecular structure or a material possessing such groups has been incorporated into the bulk resin in order for chemical bonding to occur by reaction with other chemically reactive groups present in the thermoset resin-forming composition providing the thermoset resin layer of the laminate.
These approaches to obtaining chemical bonding between a rigid thermoplastic layer and a thermoset resin layer are subject to a variety of drawbacks. If, on the one hand, the rigid thermoplastic resin must possess chemically reactive functional groups as part of its bulk molecular structure, such a requirement will greatly narrow the field of suitable resins providing this layer of the laminate since relatively few rigid thermoplastic resins possess chemically reactive functional groups. Furthermore, the presence of chemically reactive groups in the bulk thermoplastic resin is generally undesirable as these tend to enter into extraneous reactions which can degrade the mechanical, chemical and/or esthetic properties of the resin and the laminate layer formed therefrom. On the other hand, if a material possessing chemically reactive functional groups is incorporated into a chemically inert rigid thermoplastic resin, there is always the possibility that over time, the added material will prove to be incompatible with the host resin such that sooner or later, delamination will result. And, of course, the problem of extraneous reactions to which the chemically reactive groups are liable constitutes still another drawback to this approach to achieving chemical bonding in a laminate. Perhaps because of these disadvantages, laminates possessing chemically bonded layers have had limited application. Most chemically bonded laminates have been based on fairly specialized chemistry which is not readily generalized for other applications.
A variety of procedures are known for treating the surfaces of polymeric materials to improve their bondability or adherence to other materials including dissimilar polymers. These procedures include treating the exposed surfaces of polymeric materials with chemical reagents, plasmas or other types of electron bombardment to modify the molecular structure of the surface polymer without affecting the bulk properties of the resin. However, it is believed that heretofore, none of these surface treatment procedures have been utilized in the manufacture of a polymeric resin laminate in which a rigid thermoplastic resin layer is chemically bonded to a thermoset resin layer.